In industrial measurements technology, especially in automation and process control technology, field devices are regularly applied, which, in the course of a process, measure (sensors) process variables or control (actuators) control variables.
Field devices include measuring devices measuring e.g. flow, fill level, pressure, pressure difference and/or temperature. They are, as a rule, arranged decentrally, in the immediate vicinity of the process component to be measured or controlled, and deliver a measurement signal corresponding to the measured value of the registered process variable. The measuring signals of the field devices are forwarded to a superordinated unit, e.g. a central, control unit, such as e.g. a control room or a process control system. As a rule, the entire process control occurs via the superordinated unit, which receives and evaluates the measuring signals of the individual measuring devices and, as a function of their evaluation, produces control signals for the actuators, which control the process flow. In this way, for example, flow through a pipeline section can be tuned by means of a controllable valve as a function of a measured flow.
A faultless, frictionless working of field devices is of great importance for the safety of applications, in which they are applied. Correspondingly, the functional ability of field devices is exactly monitored and occurring faults are displayed in the form of fault reports, e.g. as a warning or an alarm. Preferably, the field device monitors itself. Thus, the field device performs self monitoring and/or diagnosis.
For this, field devices of today can be equipped with means for performing diagnostic methods. Such are able, on the basis of input variables available in the field device, to diagnose the occurrence of certain faults or states of the field device. For this, the input variables are analyzed on the basis of evaluating methods permanently implemented in the field device and monitoring criteria indicating occurrence of the fault or state are monitored. If such a monitoring criterion is met, the field device outputs the associated diagnosis.
Field devices of this type are described, for example, in U.S. Pat. No. 6,397,114 B1. As described there field devices are able to diagnose and report predetermined faults or states on the basis of input variables available in the field device, wherein the input variables are subjected to fixedly predetermined evaluating methods, the results of which are then monitored on the basis of fixedly predetermined monitoring criteria.
Today's diagnostic methods are predetermined in the field device factory and are limited, as a rule, to the detecting of field device specific faults or states.
There are, however, a very large number of faults or states, which are application-specific and are, with today's diagnostic abilities of the field device either not registered at all or else are not sufficiently exactly analyzed, evaluated and/or interpreted.
A reason for this is that manufacturers of field devices, as a rule, do not know in advance, where and how the field device will be applied. Correspondingly, the manufacturer does not know which faults or states are relevant for the user at the location of use, and which meaning should be attributed to them there.
In these cases, users have, in the past, frequently helped themselves by loading all input variables relevant for an application-specific fault and/or state via corresponding connection lines or interfaces from the field device into a superordinated unit, e.g. a process control system, and there centrally further processed and evaluated the input variables corresponding to the requirements of the special application. This is, however, relatively complicated, since the user, for this, as a rule, must create its own software and implement such in the superordinated unit. Moreover, there arises thereby, in given cases, a not insignificant data flow between the field device and the superordinated unit, which under circumstances blocks otherwise required interfaces and/or occupies transmission capacities. A further disadvantage is that the number of input variables, which can be output via connection lines and/or interfaces from the field device, is very limited.